The purpose of this work is to determine the thermodynamic and kinetic factors which regulate the nucleation, crystal growth and maturation of calcium phosphate crystals. This will be accomplished by estimating free ionic activities in solution for all species involved in the crystallization processes and relating these terms to the observed precipitation steps. A further correlation will be made between the composition of the solution phase and the properties of the solid calcium phosphate phase in equilibrium with the solution. The effect of crystallization inhibitors on the precipitation of calcium phosphate will also be studied and the attempt will be made to elucidate their mode of action at the crystal surfaces. Emphasis will be placed upon inhibitors which naturally occur in physiological systems or which are commonly administered for therapeutic reasons.